23 Prof. Guthrie on Bubbles. [Jan. 19, 



January 19, 1865. 



Sir HENRY HOLLAND, Bart., Vice-President, in the Chair. 

 The following communications were read : 



I. "On Bubbles." By FREDERICK GUTHRIE, Esq., Professor of 

 Chemistry and Physics at the Royal College, Mauritius. Com- 

 municated by Professor STOKES, Sec. R.S. Received December 

 22, 1864. 



As it was found necessary, in considering drops*, to define the term, and 

 limit its application, so we must understand once for all in what sense and 

 under what restrictions the term bubble is to be employed. This is the 

 more necessary, because the word bubble is used even more loosely than 

 the word drop. In Plate I. fig. A, 1, 2, and 3 show the meaning of a drop 

 as we have defined and used the expression ; 4 shows the condition of a 

 bubble as it is understood in the following investigation. 



Under this limitation, a bubble XGLf only differs from a drop XL 2 Lj 

 (3, fig. A) in consisting of a gas instead of a liquid. A bubble is a mass of 

 gaseous matter compelled to assume a more or less spherical form by the 

 cohesion and weight of the liquid medium in which it is formed, and sepa- 

 rated from other matter by the action of gravity. Since, under like con- 

 ditions of pressure, all gases are lighter than all liquids, the separating 

 force is the gravity of the medium, as was the case with the drop (3, fig. A). 

 Accordingly, a bubble invariably ascends. Owing to the universal diffusion 

 of gases, no case can exist of a gas-bubble in a gaseous medium (XGG) ; 

 and for obvious reasons a solid medium is inadmissible. So defined, a 

 bubble must therefore invariably be a case of XGL. 



It is, however, worth while, in passing, to notice the construction of some 

 other bodies which are also called drops and bubbles. Thus all the states 

 of matter shown in fig. B are called, in common speech, drops or bubbles ; 

 and some of them, indeed, are one or the other, according to the aspect 

 in which they are viewed. All of the ten modifications in fig. B are very 

 common : the Nos. 1, 2, 3, 4, 5, 6 are usually called drops ; the Nos. 7, 8, 

 9, 10 are called bubbles. Nos. 4 and 5 show the two instances of what is 

 called spheroidal state. Nos. 7, 8, 9, 10 are the commonest forms of the 

 soap-bubble. Tbe equations under each figure show the possible identity 

 of two matters of the same kind. All the above ten cases are at once dis- 

 tinguishable from the true drop and bubble by the existence in them of an 

 additional factor, which is not present in the true drop or bubble, namely 

 the cohesion of &film. Such drops and bubbles may therefore be con- 

 veniently distinguished from the true ones of fig. A by being called film- 

 drops and film-bubbles. In the spurious drops 1, 2, 3, 5, the film partly 

 enclosing and restraining the drop is a film of liquid : so also in the bubble 



* See the author's Memoir on Drops, Proceedings, vol. xiii. p. 444. 

 t Where X is either solid, liquid, or gaseous. 



